1. Field of the invention
The present invention relates to a semiconductor manufacturing apparatus for manufacturing semiconductor devices, and more specifically, relates to a dry etching technique for etching semiconductor materials such as silicon and silicon oxide films using plasma into profiles corresponding to a mask pattern formed of a resist material and the like.
2. Description of the related art
In the art of dry etching, material gas is introduced into a vacuum reactor having an evacuation means, and the material gas is turned into plasma via electromagnetic waves so as to expose the sample being processed to plasma to etch the areas of the surface of the sample being processed not covered by a mask, to thereby obtain the desired profile. High frequency voltage independent from plasma generation is applied to the sample being processed, and via the high frequency voltage, ions in the plasma are accelerated toward the surface of the sample being processed, by which the etching efficiency is improved and a perpendicular processing profile is obtained (refer for example to Japanese Patent Application Laid-Open Publication No. 2002-184766, hereinafter referred to as patent document 2).
In the art of dry etching, an endpoint detection for judging whether the etching of a predetermined quantity has been completed or not is normally performed by observing the plasma emission. Actually, the end point detection is performed by monitoring the quantity of emission of the reaction products of the material being etched in the plasma or the underlayer material exposed when etching is completed. However, from viewpoints of improvement of etching accuracy and reduction of costs by simplified processes, there are demands for not completing the etching when the underlayer material is exposed, but for stopping the etching process in midway of etching a single material or immediately prior to completing the etching.
According to such demands, the end point detection of etching cannot be performed by monitoring the emission from plasma as described above, but must be performed by monitoring either the etching quantity of the material being etched directly or the residual film thickness. A method for monitoring the etching quantity of the material being etched or the residual film thickness includes receiving light reflected on the surface of the sample being processed from plasma or from an independently-disposed light source, so as to analyze the interference pattern of the light accompanying the reduction of the material being etched on the surface of the sample being processed (refer for example to Japanese Patent No. 3643540, hereinafter referred to as patent document 1).
In etching apparatuses for etching insulating film materials such as silicon oxide films, a shower plate formed of a conductor such as silicon is disposed on an opposite side of the sample being processed, and high frequency power is applied to the whole body of the conductor including the shower plate to generate plasma. Thus, it is necessary to arrange a light transmitting unit to a conductor electrode portion opposed to the sample being processed, so as to monitor the etching quantity by performing analysis of the interference pattern of light accompanying the reduction of the material being etched. In general, a light transmitting unit has a structure to conduct light to the exterior of the vacuum reactor via a light guide rod formed for example of quartz or sapphire, and then to conduct the light via an optical fiber to a light interference pattern analysis unit composed for example of a spectroscope.
If the light guide formed for example of quartz or sapphire as the light transmitting unit is exposed directly to the shower plate surface formed for example of silicon, the end surface of the light guide rod is consumed by accelerated ions from the plasma or is subjected to deposition, making it impossible to receive light in an extremely short time. In order to overcome the problem, patent document 1 discloses a structure in which a plurality of penetrating holes 115B through which plasma cannot pass are formed to a portion of the silicon shower plate, and an optical transmitting rod 141 is arranged on the rear side of the shower plate.
According to the prior art example having the above-described structure, it becomes possible to significantly elongate the life for receiving light compared to when the light guide rod is directly exposed to plasma.
However, even by adopting the structure illustrated in patent document 1, it becomes difficult to receive light in approximately 100 to 200 hours of discharge time, which is an insufficient life according to the level of production performed in some semiconductor devices. Further, by taking measures such as reducing the diameter of the through holes formed to the shower plate and improving the aspect ratio, it becomes possible to extend the life of the light transmitting unit for some time, but the quantity of light passing therethrough is reduced, and the required accuracy cannot be ensured.
Further, in volume-production processes of semiconductors, it becomes necessary to replace the light guide rod when the light transmission rate of the rod is deteriorated. However, the prior art method has a drawback in that the replacement operation could not be performed easily.